Typical three-phase electrical distribution busways include a housing, an A-phase busbar, a B-phase busbar, a C-phase busbar and a neutral busbar, where all of the busbars have substantially the same cross-sectional area. Examples of these types of busways are found in U.S. Pat. Nos. 5,151,043 and 3,391,378. Under conditions where a busway is providing electrical power to a substantially overall balanced linear load, the fundamental 60 Hz portion of the phase currents should cancel each other in the neutral busbar. However, where a busway is providing power to an overall load which has non-linear and unbalanced components, the electrical current in the neutral busway can exceed the phase currents. As a result, unacceptable heating of the neutral busbar may occur.
It is believed that non-linear loads (e.g. power supplies, motor drives, computers, printers, etc.) cause unacceptable electrical current levels in the neutral busbars of a three-phase system as a result of the harmonics introduced by the non-linear loads. (See, Fluke--In Tune With Power Harmonics, pp. 1-15, 1991.) More specifically, certain harmonics do not cancel, but are additive and increase the currents in the neutral busbar.
Turning now from three phase busway structures having busbars as the electrical conductors to three phase wire based power distribution arrangements typically having multi-stranded wire as the conductors, wire based arrangements also have the problem of neutral heating in response to non-linear loads. One solution which has been proposed to solve the problems caused by non-linear loads in wire based arrangements is to utilize a harmonics filter. However, the problem with a harmonics filter is that it may be cost prohibitive to include these filters in many systems.
Another solution which has been proposed for wire based arrangements is to increase the size of the neutral conductor or increase the number of neutral conductors. However, this solution may not be satisfactory for busway structures since it does not deal with a competing problem which may be introduced, namely the skin effect in solid conductors. As a result of the skin effect, the provision of bigger or additional neutral conductors may not solve the heating problem if the skin effect problems are not dealt with. In wire based arrangements, the problem of skin effect is typically not a serious consideration since multi-stranded wire is used in wire based systems.
In general, the skin effect results in the majority of the current flowing in a conductor to flow at the surface of the conductor. This effect is caused by the magnetic field produced by the current in the conductor. The magnetic field causes a resistance to current flow at the interior of the conductor which is greater than at the surface of the conductor. Accordingly, an attempt to solve the problems caused by increased currents in a neutral busbar may not be solved by only increasing the size of the busbar or using multiple busbars if the effect of the skin effects are not reduced or substantially eliminated.
In light of the problems caused by non-linear loads applied to busway, the solutions which have been suggested for wire based arrangements, and the problems which arise when applying the solutions for wired systems (i.e. skin effect), it would be useful to provide a busway system having a busbar configuration which could provide electrical power to non-linear loads without overheating the neutral busbar of a busway.